Method of predicting wear on tubes of steam generator

ABSTRACT

A method predicts an amount of wear that is expected to occur on the tubes of a steam generator as a result of vibration against another structure within the steam generator. The method includes determining a volumetric amount of material that has been worn from a location on a tube over a duration of time and employing that volume as a function of time to determine the volume of material of the tube wall that is predicted to be worn from the tube or another tube at a future time. The volumetric-based analysis enables more accurately prediction of the wear depth at a future time. This enables the plugging of only those tubes that are determined from a volumetric analysis to be in risk of breach at the future time, thus slowing the rate at which tubes of a steam generator will be plugged.

CROSS REFERENCE TO RELATED APPLICATION

The instant application claims priority from U.S. Provisional PatentApplication Ser. No. 62/194,366 filed Jul. 20, 2015, the disclosures ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field

The disclosed and claimed concept relates generally to nuclear powergeneration equipment and, more particularly, to a method of predictingan amount of wear that is expected to occur on the tubes of a steamgenerator.

2. Related Art

As is understood in the relevant art, pressurized water nuclear reactorsemploy a primary loop that includes radioactive water that flows throughthe reactor core and a secondary loop that receives heat from theprimary loop which is used to perform mechanical work. Such heat iscommunicated from the primary loop to the secondary loop by employing asteam generator having a large number of tubes that are connected influid communication with the primary loop. The steam generator alsoincludes a plenum within which the fluid of the secondary loop flowsinto contact with the exterior surfaces of the tubes of the steamgenerator. The steam generator typically additionally includesanti-vibration bars and other structures that resist or at least limitthe vibration of the tubes within the interior of the steam generator.

While such steam generators have been generally effective for theirintended purposes, they have not been without limitation. Despite theexistence of the anti-vibration bars within the interior of the steamgenerator, the tubes of the steam generator nevertheless experience acertain level of vibration and typically vibrate against theanti-vibration bars and other structures, thus resulting in frettingwear at certain locations on the exterior surfaces of the tubes. Suchwear must be monitored closely in order to avoid a situation wherein thewear would be of sufficient magnitude that the wall of a tube would bebreached, which would result in undesirable nuclear contaminationbetween the primary and secondary loops. Additionally, regulationsimposed by the United States Nuclear Regulatory commission (NRC),require the tube(s) to be physically plugged when the magnitude of thewear exceeds a value of 40% of the tube wall thickness. However, forthis example that level at which plugging is required is taken as 100%of the tube wall thickness for illustration purposes only. As such, thetubes of the steam generator are periodically inspected through the useof an eddy current sensor that is received in the tubes and that isadvanced along the tubes in a known fashion while signals from thesensor are detected and recorded. The signals from the eddy currentsensor are usable to determine, for instance, a depth of wear on theexterior of a tube at a location thereon.

By knowing the thickness of the tube wall, the wear analysis that hasheretofore been employed would rely upon a straight line depth of wearanalysis to predict wear on the tube. For instance, if at a givenprevious time it had been determined that 20% of the wall thickness hadbeen worn away at a specific location, and that at a current time 60% ofthe wall thickness had been worn away at the specific location, theanalysis would conclude that during the time interval between the twotimes at which measurements were taken, an additional 40% of the tubewall thickness had been worn away. Employing the same straight linedepth of wear analysis, this methodology would predict that at a futuretime after another time interval equal to the previous time interval,another 40% of the wall thickness would be expected to worn away. In thepresent example, such wear would include the 60% wall thickness wornaway at the current time plus an additional predicted 40% wall thicknessworn away at the future time, which would equal 100% of the wallthickness being worn away at the future time, and this indicates anundesirable breach of the tube wall.

Since such inspections typically occur during refueling of a nuclearreactor and thus are at regular time intervals, it was possible, usingthe aforementioned analysis, to determine whether certain tubes shouldbe plugged prior to the steam generator and the reactor being placedback into service. It is known, however, that the plugging of a tube ofa steam generator is undesirable because it reduces the power outputthat can be obtained from a nuclear reactor. Improvements thus would bedesirable.

SUMMARY

An improved method is usable to predict an amount of wear that isexpected to occur on the tubes of a steam generator as a result ofvibration against another structure within the steam generator. Themethod includes determining a volumetric amount of material that hasbeen worn from a specific location on a tube over a duration of time andemploying that volume of material as a function of time to determine thevolume of material of the tube wall that is predicted to have beenremoved from the tube due to wear at a future time. By employing avolumetric-based analysis rather than merely a straight line depth ofwall thickness analysis, it is possible to more accurately predict whatwill be the wear depth at a future time. This advantageously enables theplugging of only those tubes that are determined from a volumetricanalysis to be in risk of breach at the future time, or exceeding theplugging requirement at the future time, thus slowing the rate at whichtubes of a steam generator will be plugged.

Accordingly, as aspect of the disclosed and claimed concept is topredict an amount of wear that is expected to occur on a tube of a steamgenerator.

Another aspect of the disclosed and claimed concept is to employ such amethod in determining whether a tube of a steam generator whosepotential wear has not been assessed can be assumed to remain viableuntil its next scheduled inspection time.

Another aspect of the disclosed and claimed concept is to provide suchan improved method that employs the volume of the material removed fromthe wall of the tube rather than merely relying upon the depth of thematerial removed to perform a linear analysis of wear to avoid prematureplugging of the tube.

Accordingly, an aspect of the disclosed and claimed concept is toprovide an improved method of predicting an amount of wear that isexpected to occur on one or more tubes from among a plurality of tubesof a steam generator as a result of vibration against another structureof the steam generator. The method can be generally stated as includingdetermining a durational volumetric amount of material that has beenworn from a given location on at least one tube from among the pluralityof tubes over a duration of time, determining a current wear state of aparticular tube from among the plurality of tubes, the current wearstate including a current volumetric amount of material that has beenworn from a particular location on the particular tube compared with anew condition, determining a predicted wear state at the particularlocation, the predicted wear state including a future volumetric amountof material that is predicted to be worn from the particular location ata future time, the future volumetric amount being based at least in partupon the current volumetric amount and the durational volumetric amount,determining based at least in part upon the predicted wear state apredicted wear depth that is predicted to exist at the particularlocation at the future time, and plugging the particular tube responsiveto the predicted wear depth meeting a predetermined threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the disclosed and claimed concept can begained from the following Description when read in conjunction with theaccompanying drawings in which:

FIG. 1A is a schematic depiction of a steam generator and a tube thereinat a first time T1;

FIG. 1B is a view of a tube of the steam generator of FIG. 1A at asecond time T2 subsequent to the first time;

FIG. 2 is a graph depicting removed volume versus wear depth;

FIG. 3 is a graph depicting tube wall percentage wear depth versusremoved volume; and

FIG. 4 is a flowchart depicting certain aspects of an improved method inaccordance with the disclosed and claimed concept.

Similar numerals refer to similar parts throughout the Specification.

DESCRIPTION

A steam generator 4 is schematically depicted in FIG. 1A. The steamgenerator 4 is in fluid communication with the primary and secondaryloops of a nuclear power plant and includes a plurality of tubes 8 thatinclude a tube 12 that is depicted in FIG. 1A. The steam generator 4additionally includes a number of other structures internal thereto thatinclude a number of anti-vibration structures that include ananti-vibration bar 16 that is depicted in FIG. 1A in proximity to thetube 12. As employed herein, the expression “a number of” and variationsthereof shall refer broadly to any non-zero quantity, including aquantity of one.

The exemplary tube 12 includes a wall 14 having an exterior surface 20at which wear occurs due to its vibrational engagement with theanti-vibration bar 16. Specifically, FIG. 1A depicts the exemplary wearas having occurred at a wear location 32 that is situated at a specificlocation along the length of the tube and at a certain circumferentiallocation about the circumference of the tube 12. In this regard, it isunderstood that the anti-vibration bar 16 that is depicted in FIG. 1A isof only a limited depth into the plane of the page of FIG. 1A, and thusthe wear that is depicted on the tube 12 in FIG. 1A is occurring onlyalong a limited portion of the length of the tube 12. The tube 12additionally has an original inner diameter 24 and an original outerdiameter 28 that are in existence at the time of manufacture of the tube12 and prior to the steam generator 4 being placed into service. Anoriginal wall thickness 36 thus can be derived from the original innerand outer diameters 24 and 28 and is depicted in FIG. 1A as extendingbetween an inner surface of the tube 12 and a portion of the exteriorsurface 20 that has not been worn away due to contact with theanti-vibration bar 16.

As noted above, FIG. 1A reflects a certain amount of wear on the tube 12at a time T1 it being understood that the time T1 is a certain period oftime after the steam generator 4 was placed into service, and that tube12 thus has a certain amount of wear at the wear location 32 at the timeT1. More specifically, the tube 12 is depicted in FIG. 1A as having awear level at time T1 as indicated at the numeral 40 and that is theportion of the original wall 14 that has been removed due to vibrationengagement between the tube 12 and the anti-vibration bar 16 at the wearlocation 32. It is assumed in FIGS. 1A and 1B that the engagementbetween the tube 12 and the anti-vibration bar 16 results in a wearpattern that is of a planar shape, but this is not intended to belimiting and rather is merely provided as an example. Wear patterns ofother shapes can be evaluated according to the teachings presentedherein without departing from the spirit of the present concept.

FIG. 1A also indicates at the numeral 44 a representation of thematerial that has been worn away from the tube 12 at the wear location32 as of the time T1. It is understood that the material 44 is intendedmerely to represent the volume of material that has been worn away fromthe tube 12 at the time T1 and is not intended to suggest that thematerial that has been removed from the tube at the time T1 was wornaway as an individual piece of material. Rather, the wear would haveoccurred over the course of time prior to the time T1 and would havebeen removed in extremely small amounts, perhaps approximatelymicroscopic amounts, with successive engagements of the tube 12 with theanti-vibration bar 16 as the tube 12 had vibrated within the steamgenerator 4.

The improved method described herein advantageously recognizes that thetube 12 engages the anti-vibration bar 16 with a fixed level of energythat is substantially unvarying. That is, as the tube 12 vibrates, itstrikes or rubs against or otherwise engages the anti-vibration bar 16with the same amount of energy at all times. Since the amount of energywith which the tube 12 engages the anti-vibration bar 16 directlyrelates to the volumetric amount of material that is removed from thetube 12 with each such engagement, the engagement between the tube 12and the anti-vibration bar 16 removes from the tube 12 the materialthereof at a fixed volumetric rate as a function of time.

At the time T1, therefore, as the eddy current sensor is receivedthrough the tube 12, the signals that are received from the eddy currentsensor enable a technician or other individual to determine the wearlevel 40, which is the depth of wear into the tube 12 at time T1. Thisdepth of wear 40 can be used in conjunction with other data, such as thegraph of FIG. 2, to determine the amount of volume of the material 44 ofthe tube 12 that has been removed from the tube 12 at the time T1. Forinstance, it might be determined that the depth of wear of time at T1 is0.009 inches of material removed from the tube 12. This wouldcorrespond, from FIG. 2, with a volume of removed material ofapproximately 0.00046 inches³. As can be seen in FIG. 3, an amount ofremoved volume equal to 0.00046 inches³ corresponds with a wear depth of20% of the wall thickness, meaning that 20% of the wall thickness hasbeen worn away.

It is noted that the graphs in FIGS. 2 and 3 are for an exemplary 0.75inch OD tube having a wall thickness of 0.043 inches when new. The datain the graphs in FIGS. 2 and 3 can be obtained in any of a variety ofways, such as mathematically or with the use of software programs, byway of example, and are very easy to derive.

FIG. 1B depicts the tube 12 at a time 12 that is subsequent to the timeT1. FIG. 1B depicts at the numeral 48 a depth of wear of the tube 12 atthe time T2 and further depicts at the numeral 52 a representation ofthe volumetric amount of material that has been worn away from the tube12 as of the time T2 due to wear against the anti-vibration bar 16.Again, it is understood that the material 52 is merely a representationof the volumetric amount of the material of the wall 14 of what has beenremoved over time due to wear and is not intended to suggest that thematerial would have been removed as a single piece of material. Ratherit is understood that the representation of the material that isindicated at the numeral 52 is meant to represent a number of additionalengagements between the tube 12 and the anti-vibration bar 16 betweenthe times T1 and T2 which has resulted in additional wear on the tube 12at the wear location 32.

In the example presented in FIG. 1B, the eddy current sensor data mighthave determined that the wear depth at the wear location 32 at the timeT2 is equal to 0.026 inches of material removed from the wall 14. If thewear depth is determined to be equal to 0.026 inches, FIG. 2 wouldindicate that the corresponding removed volume of material from the tube12 at time T2 equals 0.00236 inches³. FIG. 3 would suggest that 0.00236inches³ of removed volume of the tube 12 corresponds with 60% total weardepth. In this regard, it is understood that 0% wear depth would referto a new condition for the tube 12, and that 100% wear depth indicates abreach in the wall of the tube 12. Between the time T1 and the time T2,it can be seen that the exemplary wear went from 20% wear depth at timeT1 to 60% wear depth at time T2 for an increase in the wear depth of 40%between time T1 and time T2.

It may be desirable to predict, for example, the wear state that isexpected to exist at the wear location 32 on the tube 12 at a futuretime T3 that is subsequent to time T2. For the purposes of providing anexample, it will be assumed that the duration of time between T2 and T3is equal to the duration of time between time T1 and time T2. In thisregard, it is noted that nuclear reactors are refueled on a regularbasis, typically with an equal time between each refueling operation. Ifone were to rely open the previously known analysis methodology andconsider only the depth of the wear at the wear location 32, one mightemploy a straight line analysis based upon the wear depth at T1 and thewear depth at T2 to guess at a wear depth at T3 by adding to the weardepth at T2 (which is 60% wear depth) an additional wear depth thatwould be expected to occur between time T2 and time T3. Since theinterval between time T1 and time T2 is equal to the time intervalbetween time T2 and time T3, the straight line wear depth analysis wouldadd to the 60% wear at time T2 an additional 40% wear depth at time T3to equal 100% wear depth at T3. If this analysis were followed, it wouldindicate that the tube 12 should be plugged prior to time T3, if thewear depth which requires plugging were equal to 100%. If, for instance,time T3 were the next planned outage for the steam generator 4 after thetime T2, this would indicate that the tube 12 is in need of beingplugged at the time T2 and prior to the steam generator 4 being placedback in service. This would be undesirable because the improvedvolumetric analysis that is set forth below would instead suggest thatthe tube 12 need not be plugged at the time T2. It is reiterated thatthe aforementioned regulation by the NRC requires that a tube should beplugged prior to reaching 40% wear, and it is thus expressly noted thatthe amounts of wear mentioned herein are merely for purposes ofillustration of the advantageous concepts disclosed and claimed hereinand are not intended to be limiting and are not intended to illustratecompliance with NRC requirement.

That is, from a volumetric standpoint, it can be determined from thewear volume of 0.00046 cubic inches at time T1 and the wear volume of0.00236 cubic inches at time T2 that during the interval between time T1and time T2, 0.00190 cubic inches of material was removed from the tube12 at the wear location 32. This can be referred to as a durationalvolumetric amount of material that has been worn away from the tube 12at the wear location 32 over the duration of time between the times T1and T2. If, as is assumed herein, the time duration between times T1 andT2 is equal to the time duration between times T2 and T3, the predictedwear state at time T3 can be determined by adding to the current wearstate of the tube 12 at time T2 the durational volumetric amount ofmaterial. That is, in the depicted example, the current wear state isthe wear state of the tube 12 at time T2 which, as set forth above, iswith 0.00236 cubic inches of material having been removed from the tube12 at time T2. By adding to this the durational volumetric amount of0.00190 cubic inches, a future volumetric amount of material can becalculated to be 0.00426 cubic inches of material that is predicted tohave been worn away from the tube 12 at the time T3. From FIG. 3, it canbe seen that a removed volume of 0.00426 cubic inches corresponds with awear depth percent of only 90%, which is below the 100% that would havebeen obtained by employing merely a straight line depth wear analysis.That is, by employing a volumetric analysis, it will be unnecessary inthe indicated example to plug the tube 12 in advance of the time T3, andrather the tube 12 can be plugged in advance of a later time subsequentto the time T3.

It is reiterated that in the example that is presented herein the timeduration between time T1 and time T2 is equal to the time durationbetween time T2 and time T3. If the duration between time T2 and time T3were instead greater or less than the time duration between time T1 andtime T2, a correspondingly proportionally decreased or increasedproportion of the durational volumetric amount can be added to thecurrent wear state. For instance, if the duration between time T2 andtime T3 was equal to 1.1 times the duration of time between time T1 andtime T2, the predicted wear state could be obtained by adding 1.1 timesthe durational volumetric amount, which would be 0.00209 cubic inches tothe current wear state of 0.00236 cubic inches of material removed fromthe tube 12 to result in a total predicted wear of 0.00445 cubic inchesof material removed and a wear depth from FIG. 3 of 92%. These exemplarycalculations are provided for purposes of illustration and obviously donot employ the significant figure analysis that typically would be usedwhen combining such values.

It thus can be seen that the volumetric analysis that is presentedherein would enable the tube 12 to remain unplugged prior to time T3whereas the straight line depth of wear analysis would incorrectlysuggest that the tube 12 would have needed to be plugged. The improvedvolumetric analysis set forth herein desirably avoids premature pluggingany of the tubes of the steam generator 4.

An improved flowchart that depicts certain aspects of the improvedmethod is depicted generally in FIG. 4. Processing can begin, as at 106,where a durational volumetric amount of material that has been worn froma given location on at least one tube over a duration of time can bedetermined In the example presented above, the durational volumetricamount was determined by subtracting the current wear state of 0.00236cubic inches of material having been removed from the tube 12 at time T2from the previous volumetric amount of material that had been removedfrom the tube 12 at time T1 which was 0.00046 cubic inches, thusresulting in a durational volumetric amount of 0.00190 cubic inches ofremoved material for the time duration between times T1 and T2.

Processing then continues, as at 110, where at a current time a currentwear state is determined for a particular tube such as the tube 12, withthe current wear state including a current volumetric amount of materialthat has been removed by wear from a particular location on theparticular tube compared with a new condition. This was calculated inthe example presented above by employing the eddy current sensor todetermine that at the time T2 the current amount of material that hadbeen removed from the tube 12 since its new state was 0.00236 cubicinches.

Processing then continues, as at 114, where a predicted wear state atthe particular location is determined, with the predicted wear stateincluding a future volumetric amount of material that is predicted to beworn from the particular location at a future time, and with the futurevolumetric amount being based at least in part upon the currentvolumetric amount and the durational volumetric amount. In the examplepresented above, this was done by adding to the current volumetricamount of 0.00236 cubic inches of removed material the durationalvolumetric amount of 0.00190 cubic inches of removed material to resultin a predicted wear state at the future time of 0.00236+0.00190=0.00426cubic inches of material that is predicted to be removed from the tube12 at the time T3.

Processing then continues, as at 118, where a predicted remaining weardepth is determined based at least in part upon the predicted wearstate, with the predicted wear depth being predicted to exist at theparticular location at the future time. This was done in the examplepresented above by consulting FIG. 3 and determining that 0.00426 cubicinches of removed volume from the tube 12 corresponded with a wear depthof 90%. Processing would continue, as at 122, where at a time prior tothe future time the particular tube 12 would be plugged if the exceeds apredetermined threshold which, in the described example, is a wearingaway of 100% of the thickness of the wall of the tube 12. Since thepredicted wear state was a wear depth of only 90% of the tube 12 wall attime T3, plugging of the tube 12 was not indicated. It is noted thatinstead of plugging the tube only if the prediction suggests that thepredicted tube wear will breach the tube, it is possible to employ someother threshold, such as plugging the tube if the predicted wear wouldbe, say, 80% at the future time. Other thresholds can be employedwithout departing from the spirit of the disclosed and claimed concept,and it is reiterated that the NCR regulation would impose a pluggingthreshold of 40% wear depth. Other embodiments may then permit the tubeto never require plugging as while the volume of removed tube materialis constant, a maximum depth of wear may be associated a given tube. If,for example, the tube were to experience maximum amplitude of vibrationof 0.0258 inches, which is associated with a wear depth of 60%, thestraight line depth approximation would require the tube to be pluggedfor a plugging requirement of 100%. As the volumetric approximationwould not predict that a depth of 100% is achieved at the next duration,and the eddy current analysis at the next duration indicates a weardepth of 60%, or 0.0258 inches, the inspection result would suggest thatno further wear depth progression will be experienced and the tube canremain operational, thus never requiring plugging.

It thus can be seen that the volumetric analysis presented herein avoidsthe need to prematurely plug tubes by plugging tubes only when it ispredicted that 100% of the wall thickness or other predetermined amountof the wall thickness based on a volumetric analysis has been removedfrom the wall. This advantageously avoids the need to prematurely plugtubes and likewise avoid prematurely unnecessary reducing power outputfrom a nuclear reactor.

It is expressly noted that while the exemplary tube 12 is depicted inboth Figs. 1A and 1B, it is understood that the data from one tube 12 ofthe steam generator 4 can be used to predict wear on a separate tube 12of the steam generator 4. For instance, it is understood thatinspections of the plurality of tubes 8 of the steam generator 4 do notnecessarily occur with each shutdown and refueling of the nuclearreactor. Rather, inspections are typically only done at every thirdrefueling, and the inspection typically is only as to approximatelyone-half of the tubes from among the plurality of tubes 8. It istherefore possible that a given tube in the steam generator 4 might notactually be inspected until the sixth refueling of the reactor. However,it is possible to employ the wear on one tube to predict the wear onanother tube. For example, the wear on the tube 12 in FIG. 1A might bethe wear that was determined by eddy current analysis to exist in a tube12 at the third refueling of the nuclear reactor. It might also bedetermined that the wear as indicated in FIG. 1B is the wear thatexisted on the same tube or on another tube at the sixth refueling ofthe nuclear reactor. If the two tubes 12 in FIGS. 1A and 1B are eitherthe same tube or are assumed to have comparable vibrationcharacteristics and thus comparable wear rates, the difference in wearbetween the tube in FIG. 1A and the tube in FIG. 1B can be employed todetermine the durational volumetric amount of material that has beenworn over a duration of time, and this information is usable to projectwear on all similar tubes of the steam generator 4. For instance, fromthe foregoing analysis, it was determined that the wear at time T3 wouldbe only approximately 90% wear depth of the original wall thickness,which did not indicate a need for plugging of the tube prior to time T3,for a hypothetical plugging requirement that requires plugging onlyprior to a wear depth of 100%. If the time duration between the tube ofFIG. 1A and the tube of FIG. 1B is an additional three refuelings of thenuclear reactor, this would suggest that any of the tubes in the steamgenerator 4 that have similar vibration characteristics to the tubesthat are depicted in FIGS. 1A and 1B would not need to be the subject ofa plugging operation prior to the ninth refueling operation because anadditional three refueling operations beyond the sixth refuelingoperation represented in FIG. 1B will result in only at most about 90%wear depth at the wear location 32 and at the other wear locations onthe other tubes 12. As such, the data gleamed from a limited number oftubes 12 of the plurality of tubes 8 enables broad-based predictions onwear and performance, which is desirable.

The improved method set forth above can be implemented on any type ofcomputing device such as a general purpose computer that might receiveeddy current data as an input that is received via an input apparatusand that can perform operations on such inputs using a processorapparatus to result in outputs that may be in the form of an instructioneither to plug a given tube or to refrain from plugging a given tube.Such manipulations can be performed by routines that are stored in astorage of the processor apparatus and that are executed on a processorof the processor apparatus.

Accordingly, the improved method reduces unnecessary reductions in thepower generation capability of a nuclear reactor by avoiding unnecessaryplugging of tubes of a steam generator. The advantageous volumetricanalysis that is employed to avoid such unnecessary plugging of tubes isa more accurate evaluation of wear mechanisms and is thus desirablyemployed.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular embodiments disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the foregoing disclosure.

What is claimed is:
 1. A method of predicting an amount of wear that isexpected to occur on one or more tubes from among a plurality of tubesof a steam generator as a result of vibration against another structureof the steam generator, the method comprising: determining a durationalvolumetric amount of material that has been worn from a given locationon at least one tube from among the plurality of tubes over a durationof time; determining a current wear state of a particular tube fromamong the plurality of tubes, the current wear state including a currentvolumetric amount of material that has been worn from a particularlocation on the particular tube compared with a new condition;determining a predicted wear state at the particular location, thepredicted wear state including a future volumetric amount of materialthat is predicted to be worn from the particular location at a futuretime, the future volumetric amount being based at least in part upon thecurrent volumetric amount and the durational volumetric amount;determining based at least in part upon the predicted wear state apredicted wear depth that is predicted to exist at the particularlocation at the future time; and plugging the particular tube responsiveto the predicted wear depth meeting a predetermined threshold.
 2. Themethod of claim 1, further comprising: performing the determining of thecurrent wear state at a current time prior to the future time; andperforming the plugging at a time subsequent to the current time butprior to the future time.
 3. The method of claim 1, further comprisingemploying the particular tube as the at least one tube.
 4. The method ofclaim 1, further comprising: performing the determining of the currentwear state at a current time, the future time being a period of timesubsequent to the current time; and calculating the future volumetricamount by adding together the current volumetric amount and aproportional portion of the durational volumetric amount thatcorresponds with the ratio of the period of time to the duration oftime.
 5. The method of claim 1, further comprising: performing on thesteam generator an inspection operation on fewer than all of the tubesof the plurality of tubes wherein a given tube other than the particulartube and the at least one tube is uninspected during the inspectionoperation; predicting a predicted wear condition on the given tube thatincludes a predicted volumetric amount of material that is predicted tobe worn from a given location on the given tube at the future time, thepredicted volumetric amount being based at least in part upon thecurrent volumetric amount and the durational volumetric amount;determining based at least in part upon the predicted wear condition acalculated wear depth that is predicted to exist at the given locationat the future time; and operating the steam generator without pluggingthe given tube responsive to the calculated wear depth not meeting apredetermined threshold.
 6. The method of claim 1, further comprising:performing the determining of the current wear state at a current time,the future time being a period of time subsequent to the current time;and calculating the predicted volumetric amount by adding together thecurrent volumetric amount and a proportional portion of the durationalvolumetric amount that corresponds with the ratio of the period of timeto the duration of time.